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Wood chip denitrification bioreactors can reduce nitrate in tile drainage

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Abstract

Widespread contamination of surface water with nitrate-nitrogen (NO3-N) has led to increasing regulatory pressure to minimize NO3-N release from agricultural operations. We evaluated the use of wood chip denitrification bioreactors to remove NO3-N from tile drain effluent on two vegetable farms in Monterey County. Across several years of operation, denitrification in the bioreactors reduced NO3-N concentration by an average of 8 to 10 milligrams per liter (mg L−1) per day during the summer and approximately 5 mg L−1 per day in winter. However, due to the high NO3-N concentration in the tile drainage (60 to 190 mg L−1), water discharged from the bioreactors still contained NO3-N far above the regulatory target of < 10 mg L−1. Carbon enrichment (applying soluble carbon to stimulate denitrifying bacteria) using methanol as the carbon source substantially increased denitrification, both in laboratory experiments and in the on-farm bioreactors. Using a carbon enrichment system in which methanol was proportionally injected based on tile drainage NO3-N concentration allowed nearly complete NO3-N removal with minimal adverse environmental effects.

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... In a few studies (Hartz et al., 2017;Jansen et al., 2019;Roser et al., 2018), the addition of soluble carbon to bioreactors improved nitrate removal rates, particularly in bioreactors with aged woodchips where initial removal rates had decreased. Denitrification rates were enhanced by liquid carbon sources such as ethanol, glycerine, acetate, and methanol, which provided denitrifiers a more readily available carbon energy source (Hartz et al., 2017;Jansen et al., 2019;Roser et al., 2018). ...
... In a few studies (Hartz et al., 2017;Jansen et al., 2019;Roser et al., 2018), the addition of soluble carbon to bioreactors improved nitrate removal rates, particularly in bioreactors with aged woodchips where initial removal rates had decreased. Denitrification rates were enhanced by liquid carbon sources such as ethanol, glycerine, acetate, and methanol, which provided denitrifiers a more readily available carbon energy source (Hartz et al., 2017;Jansen et al., 2019;Roser et al., 2018). Hartz et al. (2017) demonstrated that constant methanol dosing increased denitrification rates, resulting in complete nitrate removal in a mesocosm experiment and a field-scale bioreactor with a 2-day hydraulic retention time (HRT) and high nitrate inflow concentrations mg N L − 1 ). ...
... Denitrification rates were enhanced by liquid carbon sources such as ethanol, glycerine, acetate, and methanol, which provided denitrifiers a more readily available carbon energy source (Hartz et al., 2017;Jansen et al., 2019;Roser et al., 2018). Hartz et al. (2017) demonstrated that constant methanol dosing increased denitrification rates, resulting in complete nitrate removal in a mesocosm experiment and a field-scale bioreactor with a 2-day hydraulic retention time (HRT) and high nitrate inflow concentrations mg N L − 1 ). With methanol dosing, the equivalent nitrate removal rate of ~36 g N m − 3 d − 1 was much higher than ~9 g N m − 3 d − 1 without methanol dosing in control bioreactors. ...
Article
Denitrifying bioreactors are effective tools for removing nitrate from agricultural drainage water. However, as woodchips age with time, a shortage of labile carbon supply limits nitrate removal by microbial denitrification when high nitrate pulses occur in drainage waters. In this study, we investigated the potential of methanol dosing at a constant rate to increase nitrate removal rates in a 58 m³ pilot-scale bioreactor (25 m³ saturated volume) installed on a dairy farm for two consecutive drainage seasons. The drainage water in the bioreactor had a mean hydraulic retention time (HRT) of 12.7 days and 13.5 days in the 2020 and 2021 drainage seasons. With 14.4 L of methanol solution (8% v/v) added per day, the seasonal nitrate removal rates were 8.6 g N m⁻³ d⁻¹ in 2020 and 5.1 g N m⁻³ d⁻¹ in 2021 when the methanol dosing rate was halved. Both rates (2020 and 2021) were enhanced as compared to seasonal rates of 0.67–1.60 g N m⁻³ d⁻¹ in previous years (2017 and 2018) when the bioreactor was not dosed. When there were very large pulses of nitrate into the bioreactor, which exhausted added methanol, nitrate was observed at concentrations above limiting ranges (> 3 mg N L⁻¹) at the outlet on several occasions in 2021. Cumulative nitrate load reductions of 1859 g N and 1620 g N occurred in 2020 and 2021, respectively, resulting in overall nitrate removal efficiencies of 85 and 73%, respectively. Methanol concentrations decreased by order of magnitude along the bioreactor length, from mean inlet concentrations of 327 mg CH3OH-C L⁻¹ in 2020 (higher dosing rate) to concentrations of <50 mg CH3OH-C L⁻¹ at the outlet. The mean methanol removal rates of 106 g CH3OH-C m⁻³ d⁻¹ in 2020 and 109 g CH3OH-C m⁻³ d⁻¹ in 2021. A 90% (2020) and 100% (2021) overall methanol removal efficiency was calculated. With methanol dosing, sulfate removal occurred in the bioreactor, with an average sulfate removal rate of 8.5 g SO4²⁻-S m⁻³ d⁻¹ in 2020 and 0.5 g SO4²⁻-S m⁻³ d⁻¹ in 2021. This work demonstrated that methanol additions to bioreactors could enhance denitrification rates even when nitrate was limiting without considerable losses of methanol being released to the receiving waters.
... A few studies have shown that adding a soluble organic carbon source (e.g., ethanol, methanol, acetate, and succinate) to woodchip bioreactors improves nitrate removal rates (Hartz et al., 2017;Jansen et al., 2019;Palomo et al., 2013;Roser et al., 2018). Palomo et al. (2013) found that adding succinate (C 4 H 6 O 4 ) as an external carbon source enhanced nitrate removal efficiency in a field denitrification wall treating groundwater flow from 15% to 73%. ...
... These improved nitrate removal rates were compared to control rates of 7.1 ± 3.8 g N m − 3 day − 1 (mean ± SD) without carbon dosing under the same operating circumstances (i.e., same temperature and hydraulic conditions). Hartz et al. (2017) studied the effects of carbon dosing on laboratory-scale bioreactors (14 L) with two different loads of methanol and glycerin. The study reported removal efficiency improvements of 78% and 100% in methanol-dosed bioreactors and 75% and 100% in glycerine-dosed bioreactors, respectively, compared to 5% in woodchip bioreactors. ...
... g N m − 3 day − 1 without methanol dosing in the same bioreactor (Rivas et al., 2020). While Moghaddam et al. (under review) demonstrated a substantial increase in nitrate removal rates with methanol dosing, the nitrate removal rates were considerably different from other carbon dosing studies (Hartz et al., 2017;Jansen et al., 2019;Roser et al., 2018). The variations in nitrate removal rates between the prior dosing studies and those of Moghaddam et al. (under review) were most likely attributable to differences in scale of operation, environmental conditions, and bioreactor inputs. ...
Article
The nitrate removal efficiency of denitrifying bioreactors decreases when the carbon supply from woodchips is insufficient, particularly during large nitrate pulses. This study aimed to assess the effects of methanol dosing, as an external carbon source, on nitrate removal rates in mesocosm-scale bioreactors while monitoring the secondary effects of dosing that may occur. A secondary goal was to quantify sulfate reduction rates and methanol consumption in the presence and absence of nitrate to aid in determining the dosing load to minimize undesirable effects such as methanol entering receiving waters and minimizing sulfate reduction. We continuously dosed the bioreactors with nitrate (∼20 mg NO3⁻-N L⁻¹), methanol (∼35 mg CH3OH-C L⁻¹), and sulfate (∼9 mg SO4²⁻-S L⁻¹), which was already present in the tap water. In a long-term controlled mesocosm experiment, we established three bioreactor treatments to investigate nitrate, methanol, and sulfate removal rates with and without the presence of nitrate and methanol. Compared to the woodchip control treatment, methanol dosing resulted in an approximately fourfold increase in nitrate removal rates from 7 to 27 g N m⁻³ day⁻¹. Methanol dosing increased sulfate removal rates, from average sulfate removal rates of 1.5 g SO4²⁻-S m⁻³ day⁻¹ under nitrate-prevailing conditions to 5.5 g SO4²⁻-S m⁻³ day⁻¹ removal rates under nitrate-limiting conditions compared to woodchip control removal of 0.3 g SO4²⁻-S m⁻³ day⁻¹. Mean methanol removal rates were 23 g CH3OH-C m⁻³ day⁻¹ under nitrate-prevailing conditions compared to 18 g CH3OH-C m⁻³ day⁻¹ in the woodchip control experiment. Improved nitrate removal rates, as well as methanol consumption and sulfate removal rates, might be leveraged to develop innovative low-footprint bioreactors.
... Although woodchip bioreactors (WBR) have been designed for treating tile-drain runoff in farmlands of the Midwest, the design and sizing concept in that region is based on gravitational flow through a subsurface structure filled with woodchips and a weir that allows for controlling retention time (Schipper et al. 2010a;Christianson et al. 2012). For fields with perched water tables, Hartz et al. 2017 proposed that an above ground WBR sized at 61 m by 16.8 m by 1.8 m would treat a 200-acre field producing 250 m 3 of water with concentrations of Nitrate-N of 60 mg L À1 being removed to achieve the drinking water standard of 10 mg L À1 . This work raises the need for further validation and development of a model for WBR sizing. ...
... Shrimali & Singh 2001;cf. Hagman et al. 2008;Hartz et al. 2017;Roser et al. 2018). Hartz et al.'s (2017) study of the addition of ethanol or glycerol to two field WBRs designed for an HRT of 2 days found that nearly complete removal of inlet nitrate concentration of 160 mg L À1 was achieved if a second carbon source was added at the ratio of 1.4:1 (C applied: N denitrified on a mass basis). ...
... Hagman et al. 2008;Hartz et al. 2017;Roser et al. 2018). Hartz et al.'s (2017) study of the addition of ethanol or glycerol to two field WBRs designed for an HRT of 2 days found that nearly complete removal of inlet nitrate concentration of 160 mg L À1 was achieved if a second carbon source was added at the ratio of 1.4:1 (C applied: N denitrified on a mass basis). Roser et al. (2018) found that by spiking woodchips with acetate in a column study, nitrate removal was increased to a rate of 30 g N m À3 day À1 at 5°C and to 121 g N m À3 day À1 at 15°C. ...
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Article
Woodchip bioreactors are capable of removing nitrate from agricultural runoff and subsurface tile drain water, alleviating human health hazards and harmful discharge to the environment. Water pumped from agricultural tile drain sumps to nearby ditches or channels could be cost-effectively diverted through a woodchip bioreactor to remove nitrate prior to discharge into local waterways. Sizing the bioreactor to achieve targeted outlet concentrations within a minimum footprint is important to minimizing cost. Determining the necessary bioreactor size should involve a hydrological component as well as reaction type and rates. We measured inflow and outflow nitrate concentrations in a pumped open-channel woodchip bioreactor over a 13-month period and used a tanks-in-series approach to model hydrology and estimate parameter values for reaction kinetics. Both zero-order and first-order reaction kinetics incorporating the Arrhenius equation for temperature dependence were modeled. The zero-order model fit the data better. The rate coefficients (k = 17.5 g N m−3 day−1 and theta = 1.12 against Tref = 20 °C) can be used for estimating the size of a woodchip bioreactor to treat nitrate in agricultural runoff from farm blocks on California's central coast. We present an Excel model for our tanks-in-series hydrology to aid in estimating bioreactor size. HIGHLIGHTS A tanks-in-series model is simple and can be used to depict hydrology and nitrate decay in woodchip bioreactors.; Zero order kinetics better depicts nitrate decay rate than first-order kinetics for agricultural runoff.; One can estimate the minimum size needed for a pumped tile-drain woodchip bioreactor to meet water quality objectives using an Excel model.;
... Since then, the suitability of fieldscale bioreactors as a mitigation option for the impacts of agricultural drainage has been investigated worldwide, such as in Canada ( van Driel et al., 2006;Husk et al., 2017), Denmark (Bruun et al., 2016b;Bruun et al., 2017;Carstensen et al., 2019), Germany (Pfannerstill et al., 2016), Ireland (Fenton et al., 2016), New Zealand (Hudson et al., 2018;Goeller et al., 2019), and the USA (Chun et al., 2010;Christianson et al., 2012a;Ghane et al., 2015;Hassanpour et al., 2017). In the US, bioreactors have already been accepted as one of the US Department of Agriculture's Conservation Practices (Standard No. 605) and are being adopted increasingly in cropped lands (Christianson et al., 2012a;Hartz et al., 2017). However, a different bioreactor design and operation than in the US is required for the shallower subsurface drainage systems in lowland areas with accompanying highly variable flows and nitrate concentrations common in many agricultural lands, including pastoral lands in New Zealand (NZ). ...
... This may well be accomplished by adding readily available carbon during periods of high flow and/or high nitrate concentrations in the inflow, as we have seen removal efficiency declining with decreasing HRT (Fig. 7a). Limited studies investigating the effect of additional carbon have shown increase in substantial nitrate removal in woodchip bioreactors with the addition of readily available carbon, such as acetate, glucose, methanol, and glycerine (Warneke et al., 2011b;Warneke et al., 2011c;Hartz et al., 2017;Roser et al., 2018). For instance, up to more than double the nitrate RRs were observed when glucose was added to the bioreactor with pine woodchips (Warneke et al., 2011c). ...
... Thus, C dosing holds promise to optimise the performance of bioreactors in treating artificial drainage water with variable flow conditions. Limited field-scale studies with C dosing were done mainly to address extremely high nitrate concentrations in the inflow (150-193 mg NO 3 -N L −1 ) (Hartz et al., 2017). Further studies are needed to provide guidance for nitrate concentrations more commonly observed under pastoral agriculture (< 30 mg NO 3 -N L −1 ) and on C dosing operation (the type of C source, frequency, amount, etc.) to minimise potential side effects, including excess DOC in the outflow (Hartz et al., 2017) and clogging by biofilms (Hunter, 2001). ...
Article
While enabling economically viable use of poorly drained soils, artificial subsurface drainage has also been found to be a significant pathway for nutrient transfers from agricultural land to surface waters. Thus, mitigating the impacts of agriculture on surface water quality needs to address nutrient transfers via subsurface drainage. Woodchip bioreactors are a promising mitigation option as demonstrated under arable agriculture in the mid-west of the USA. However, research is needed to ascertain their efficiency in removing nutrients from very flashy drainage flows common in New Zealand (NZ) pastoral agriculture and any possible pollution swapping (e.g. reduction of leaching losses vs. greenhouse gas emissions). Accordingly, a lined 78-m³ woodchip bioreactor was constructed on a dairy farm in the Hauraki Plains (Waikato, NZ) with a drainage area of 0.65 ha. Rainfall, flow, hydrochemistry and dissolved gases in the inflow and outflow were monitored for two drainage seasons (part of 2017, 2018). Based on the nitrate-N fluxes, the estimated nitrate removal efficiency of the bioreactor was 99 and 48% in 2017 and 2018, respectively. The higher removal efficiency in 2017 could be attributed to two reasons. Firstly, the substantially longer hydraulic residence time (HRT) of the water in the bioreactor (mean = 21.1 days vs 4.7 days in 2018) provided more opportunity for microorganisms to reduce the nitrate. A strong positive relationship between HRT and removal efficiency was also observed within the 2018 drainage season. Secondly, denitrification was supported in 2017 by greater electron donor availability. Evidence of this was the higher mass of DOC discharge from the bioreactor (318 mg C L⁻¹ of bioreactor volume vs 165 mg C L⁻¹ in 2018). Removal rates in the bioreactor varied from 0.67–1.60 g N m⁻³ day⁻¹ and were positively correlated with inflow nitrate loads. Pollution swapping was observed during the start-up phase of the bioreactor in both years (DOC, and DRP only in 2017) and during periods with very long HRTs (hydrogen sulphide (H2S) and methane (CH4) production). Substantially elevated discharges of DOC and DRP, as compared to inlet conditions, occurred during the initial start-up phase of the bioreactor in 2017 (3 to 3.5 pore volumes of the bioreactor), but only slightly elevated DOC and decreased DRP discharges were observed when drainage flow resumed at the start of the 2018 drainage season. Unexpectedly, cumulative DRP removal during the 2018 drainage season amounted to 89% of the DRP inflow into the bioreactor. Long HRTs (>5 days) enabled high nitrate removal efficiency (≥59%) and promoted complete reduction of nitrate to harmless dinitrogen gas but also promoted strongly reduced conditions, resulting in the production of H2S and CH4. On the other hand, short HRTs (<4 days) only allowed for moderate nitrate removal efficiency (≤43%) and constrained complete reduction of nitrate resulting in higher nitrous oxide concentrations in the outflow as compared to the inflow. Thus, nitrate removals above 50% were not able to be achieved without inducing H2S and CH4 generation. However, it may be achievable when the microbial community is provided with an additional source of readily available carbon during the critical periods when hydraulic flow and concomitant N load peaks occur.
... Another use not originally envisioned involved collaboration with the University of California Cooperative Extension in nearby agricultural fields in a feasibility study of the use of ISUS to provide a control feedback loop in an agricultural wood chip denitrification bioreactor (Hartz et al., 2017). Available real-time nitrate data were used to optimize the application of carbon enrichment to promote complete nitrate removal in an agricultural field tile drainage with minimal adverse environmental effects (Hartz et al., 2017). ...
... Another use not originally envisioned involved collaboration with the University of California Cooperative Extension in nearby agricultural fields in a feasibility study of the use of ISUS to provide a control feedback loop in an agricultural wood chip denitrification bioreactor (Hartz et al., 2017). Available real-time nitrate data were used to optimize the application of carbon enrichment to promote complete nitrate removal in an agricultural field tile drainage with minimal adverse environmental effects (Hartz et al., 2017). ...
Article
Chemical sensor development has been a focus for the Monterey Bay Aquarium Research Institute (MBARI) from its inception. Progress in chemical analyzers benefited from technological advances in many fields. MBARI’s development of a low power, reagent-free, in situ ultraviolet spectrophotometer (ISUS) for measuring dissolved nitrate has been transformative. These ultraviolet optical nitrate sensors have been deployed on remotely operated vehicles, autonomous underwater vehicles, benthic flux chambers, profiling floats, and moorings. This paper focuses on a 15+ year time series of nitrate observations on MBARI’s M1 mooring in Monterey Bay, California. The resulting data set captures seasonal and interannual variability from El Niño and La Niña, and water mass anomalies on the eastern boundary of the Pacific Ocean. The high temporal resolution (hourly) nitrate measurements additionally quantify diel cycles of nitrate uptake as a proxy for new production. The calculated f-ratio varies seasonally with relatively higher values during the lower productivity winter season. The physical supply and uptake of nitrate are dominated by upwelling in this coastal environment. An expanding number of ultraviolet optical nitrate sensor deployments on moorings and autonomous platforms such as profiling floats will provide ever-broadening coverage of the world ocean, resulting in enhanced spatial and temporal resolution of nitrate measurements and, ultimately, improved insight into the dynamics of nitrogen cycling and phytoplankton ecology throughout a changing global ocean.
... The use of liquid organic carbon sources, such as methanol and acetate, has recently been investigated as an external carbon source for bioreactors in which nitrate removal rates had declined (Roser et al. 2018;Hartz et al. 2017). However, there is a lack of understanding of field-scale bioreactor design and scaling with additional carbon sources under variable operating conditions and inputs. ...
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Conference Paper
Denitrifying woodchip bioreactors are simple ecotechnologies that could help preserve the water quality by reducing nitrate loads from both point and non-point pollution sources. These systems consist of lined pits filled with a solid carbon source (e.g., woodchips) that convert nitrate to harmless dinitrogen gas by a microbial process known as denitrification. However, due to a lack of sufficient carbon supply from the woodchips, the efficiency of the bioreactor might be overwhelmed by large nitrate input pulses, especially in bioreactors containing aged woodchips. The current research aimed to develop a simple and effective carbon dosing approach that would increase nitrate removal rates while minimizing excess losses of carbon from the system. During the 2020 and 2021 drainage seasons, a bioreactor in Waikato, New Zealand, was dosed with constant rates of methanol (serving as a supplementary carbon source). The performance of the bioreactor was compared between the two seasons as well as with data from 2018-a season in which no methanol dosing was performed. Under extremely variable flow conditions, methanol dosing considerably increased nitrate removal rates from 0.1-1.60 g N m-3 day-1 in the 2018 drainage season (undosed) to 10 g N m-3 day-1 in 2020 and 16 g N m-3 day-1 in 2021. The results also revealed a considerable drop in methanol concentrations along the length of the bioreactor (removal rates ranging from 24 to 218 g C m-3 day-1), indicating a methanol removal efficiency of greater than 99 percent. Overall, methanol dosage increased nitrate removal rates in the bioreactor, and methanol concentrations at the outlet were substantially below thresholds of concern, even when nitrate was limited as a 2 terminal electron acceptor. Therefore, while improving nitrate removal rates dramatically, constant rate methanol dosing did not result in significant methanol loss from the system.
... A few recent studies have shown that external carbon (e.g., methanol, ethanol, and acetate) dosing of bioreactors can significantly increase nitrate removal rates in bioreactors (Hartz et al., 2017;Herbert et al., 2014;Jansen et al., 2019;Roser et al., 2018). For instance, Roser et al. (2018) measured nitrate removal rates of 120.6 g N m − 3 day − 1 in acetate-dosed bioreactors. ...
Article
Denitrifying bioreactors are an effective approach for removing nitrate from a variety of non-point wastewater sources, including agricultural tile drainage. However, compared to alternate mitigation approaches such as constructed wetlands, nitrate removal in bioreactors may decline with time and low temperature, resulting in poor long-term nitrate removal rates. To address the low nitrate removal rates in bioreactors, the addition of an external carbon source has been found to be an effective method for enhancing and maintaining nitrate removal rates. While carbon dosing has led to a significant improvement in nitrate removal, some of the possible adverse effects of carbon dosing, such as clogging and reduction in hydraulic efficiency, remain unknown and need to be investigated. Using observations from both field and mesocosm trials, we compared the hydraulic performance of bioreactors with and without carbon dosing. The pilot-scale field bioreactor (58 m³ total woodchip volume, 25 m³ saturated volume, referred to as field bioreactor in this work) treated drainage water from a paddock of a dairy farm. The bioreactor received an exogenous carbon dose of 8% methanol (v/v) at 10 mL min⁻¹ and 5 mL min⁻¹ in the 2020 and 2021 drainage seasons, respectively. The field bioreactor had a statistically higher hydraulic conductivity in 2018 when not carbon-dosed of 4601 m day⁻¹, reducing to 1600 m day⁻¹ in 2021 which was the second year of carbon dosing. Field observations could not establish whether the addition of liquid carbon could affect the bioreactor's internal hydraulics performance, such as actual hydraulic retention time (AHRT), despite a significant decline in hydraulic conductivity in the field bioreactor. Separate experiments on replicated bioreactor mesocosms were conducted to investigate the effects of carbon dosing on the internal hydraulic parameters of bioreactors. These mesocosm bioreactors had previously been used to study the long-term effects of methanol dosing on bioreactor performance, such as nitrate removal under steady-state conditions. The mesocosm and field bioreactors shared some characteristics, such as the use of methanol as an external carbon source, but the mesocosm experiments were hydrologically controlled contrary to the field bioreactor's transient operating conditions. We found that methanol dosing in either carbon or nitrate limiting conditions had no significant effects (p-value >0.05) on internal hydraulic parameters (e.g., effective utilization of media) when compared to control bioreactors. The present study offers insight into the long-term hydraulic performance of bioreactors and may help develop small-footprint bioreactors that incorporate external carbon dosing.
... The color was not quantified; however, the water was visibly darker than in our previous study with a S 0 -based CDF (He et al., 2020). Hartz et al. (2017) observed that effluent from a wood chipdenitrification reactor was dark colored for the first several weeks of operation due to tannins that leached from the woodchips. Clear water could enhance the ability of fish to capture feed and allow the farmer to observe fish health, behavior, and feeding activity (Davidson et al., 2016). ...
Article
This study investigated the performance and microbiome of cyclic denitrification filters (CDFs) for wood and sulfur heterotrophic-autotrophic denitrification (WSHAD) of saline wastewater. Wood-sulfur CDFs integrated into two pilot-scale marine recirculating aquaculture systems achieved high denitrification rates (103 ± 8.5 g N/(m³·d)). The combined use of pine wood and sulfur resulted in lower SO4²⁻ accumulation compared with prior saline wastewater denitrification studies with sulfur alone. Although fish tank water quality parameters, including ammonia, nitrite, nitrate and sulfide, were below the inhibitory levels for marine fish production, lower survival rates of Poecilia sphenops were observed compared with prior studies. Heterotrophic denitrification was the dominant removal mechanism during the early operational stages, while sulfur autotrophic denitrification increased as readily biodegradable organic carbon released from wood chips decreased over time. 16S rRNA-based analysis of the CDF microbiome revealed that Sulfurimonas, Thioalbus, Defluviimonas, and Ornatilinea as notable genera that contributed to denitrification performance.
... Woodchip bioreactors have been successful at removing nitrate, with almost 100% nitrate load reductions reported in some cases (Gibert et al. 2008;Christianson et al. 2012). However, under cold temperatures (<10°C), bioreactor performance decreases due to inhibited microbial activity (Schipper et al. 2010;Warneke et al. 2011;Ghane et al. 2015;David et al. 2016;Hartz et al. 2017;Hassanpour et al. 2017;Husk et al. 2017). This is especially a concern in cooler regions such as northern Europe and the upper Midwest USA where large quantities of nitrate can leach from agricultural lands during periods when water temperatures are low (Jin and Sands 2003). ...
Article
Aims: This study was done to obtain denitrifiers that could be used for bioaugmentation in woodchip bioreactors to remove nitrate from agricultural subsurface drainage water. Methods and results: We isolated denitrifiers from four different bioreactors in Minnesota, and characterized the strains by measuring their denitrification rates and analyzing their whole genomes. A total of 206 bacteria were isolated from woodchips and thick biofilms (bioslimes) that formed in the bioreactors, 76 of which were able to reduce nitrate at 15°C. Among those, nine potential denitrifying strains were identified, all of which were isolated from the woodchip samples. Although many nitrate-reducing strains were isolated from the bioslime samples, none were categorized as denitrifiers but instead as carrying out dissimilatory nitrate reduction to ammonium (DNRA). Conclusions: Among the denitrifiers confirmed by 15 N stable isotope analysis and genome analysis, Cellulomonas cellasea strain WB94 and Microvirgula aerodenitrificans strain BE2.4 appear to be promising for bioreactor bioaugmentation due to their potential for both aerobic and anaerobic denitrification, and the ability of strain WB94 to degrade cellulose. Significance and impact of study: Denitrifiers isolated in this study could be useful for bioaugmentation application to enhance nitrate removal in woodchip bioreactors.
... Similarly, retention of DOC in biofilters or decreasing the loss of DOC into infiltration stormwater could increase their utilization for denitrification. A high concentration of DOC near the surface of biochar or woodchips could increase the kinetics of denitrification that highly depends on the concentration of dissolved organic carbon (Hartz et al., 2017). Biochar could trap DOC in pore water or in the thin film near its surface, which can be utilized by the microbial community (Ulrich et al., 2017). ...
Article
Stormwater biofilters have been increasingly used to mitigate the impact of climate change on the export of contaminants including nitrate to water bodies. Yet, their performance is rarely tested under high-intensity rainfall events, which are predicted to occur more frequently under climate change scenarios. We examined the potential of biochar to improve the resilience of woodchip biofilters under simulated high-intensity rainfall events and linked denitrification to biochar-mediated changes in hydrological (physical), chemical, and biological properties of woodchip biofilters. Results showed that nitrate removal capacity of woodchip biofilters decreased with increases in rainfall intensity or duration and decreases in antecedent drying time. However, adding biochar to woodchips significantly decreased the exhaustion rate of woodchips, only when the hydraulic residence time (HRT) was less than 5 h. At longer HRT (>5 h), the benefits of biochar became less apparent. We attributed the improved denitrification during high nitrate loading to biochar's ability to decrease dissolved oxygen in pore water and increase water holding capacity and retention of dissolved organic carbon and nitrate-all of which could increase nitrate utilization. Biochar increased the net microbial biomass but did not affect the relative abundance of denitrifying genes, which indicates that a shift in microbial biomass could not fully explain the observed increase in nitrate removal in biochar-augmented woodchip biofilters. Overall, the results showed that biochar could increase the resiliency of woodchip biofilters for denitrification in high-intensity rainfall events, a worst-case scenario, thereby mitigating the water quality degradation during climate change.
... The scalability of bioreactors to enhance nitrate removal under a variety of flow and nitrate loading scenarios, and the additional benefit of not removing land from agricultural production, makes them an attractive tool to farmers and catchment managers (Christianson et al., 2012a). Nevertheless, the effectiveness of field-scale bioreactors varies enormously, ranging between 1 and 98% mass removal of nitrate entering (Christianson et al., 2012b;David et al., 2015;Hartz et al., 2017;Hassanpour et al., 2017). While the engineering and biochemical design variables that control bioreactor performance are well documented (Addy et al., 2016), surprisingly few studies have evaluated effects of bioreactor performance on in-stream water quality or downstream ecosystem functioning (Christianson et al., 2014;Goeller et al., 2016;Weigelhofer and Hein, 2015). ...
Article
Globally, small agricultural waterways fed by springs, tile drains, and seeps can disproportionately contribute to downstream nutrient loading, which is associated with declines in water quality and ecosystem functions. Treating nitrate using a multiple tool, multiple-scale approach in small waterways could offer improved management of these sources. We used a before-after-control-impact design to test the suitability of three small (< 30 m 3) edge-of-field denitrifying woodchip bioreactors and stream bank reshaping and riparian planting. Over three-and-a-half-years, riparian rehabilitation enhanced nitrate flux attenuation compared to pre-rehabilitation , but only under relatively low flow conditions. In comparison, there were no significant changes in nitrate flux in a control waterway under any flow condition. N fluxes always increased in both the control and treatment waterways when reaches gained water downstream. Nitrate removal efficiencies for all three bior-eactors ranged from < 10 to > 99%, with performance variations due to short residence times and fluctuations in source water chemistry. A single tile drain bioreactor removed 0.41 kg NO 3-N d −1 , equivalent to ∼10% of the mean daily tile drain nitrate load. Greenhouse gas fluxes from the tile drain bioreactor were similar to the surrounding pasture (CO 2-C mean: 185-286 mg C m 2 h −1 ; N 2 ON mean: 49-90 μg N m 2 h −1), suggesting no negative impacts from the bioreactor. Overall, our results suggest a multiple-tool, multiple-scale application of rehabilitation tools can reduce downstream N fluxes, but only under certain flow conditions. Thus, local rehabilitation tools, like those trialed here, will need to be scaled appropriately if they are to significantly attenuate nutrient losses from small agricultural waterways. Moreover, these will not replace catchment-scale nutrient plans to address losses from land and legacy groundwater N pollution.
... However, making more carbon available to the microbial community during periods with high nitrate loads (high flow and/or high nitrate concentrations) may help achieve the maximum nitrate removal that is feasible without incurring substantial negative side effects. This may well be accomplished by adding readily available carbon (e.g., methanol) (Hartz et al. 2017) during periods of high flow and/or high nitrate concentrations in the inflow. As an unexpected cobenefit of the denitrifying bioreactor, substantial removal (89%) of dissolved reactive phosphorus was observed in the 2018 drainage season. ...
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Artificial drainage has been instrumental in the viable use of poorly drained soils for agriculture. However, artificial drains can also provide a pathway for fast and unattenuated nutrient transfers to streams and rivers. To remove nitrate from drainage water, bioreactors have recently been widely adopted as an edge-of-field mitigation measure, particularly in the USA. Bioreactors are fundamentally a lined pit filled with woodchips as a source of carbon, which microorganisms use to transform nitrate through the process of denitrification into gaseous forms of nitrogen, mostly N2. However, there is a lack of information on the performance of these bioreactors under the very flashy agricultural drainage flow conditions typical for New Zealand. Moreover, to avoid pollution-swapping, any possibly occurring negative side effects need to be investigated. A pilot-scale woodchip bioreactor was constructed on a dairy farm on the Hauraki Plains in Waikato and was monitored for one and half drainage seasons (part of 2017, 2018). The nitrate removal efficiency of the bioreactor, calculated from the difference in nitrate load between the bioreactor inflow and the outflow, was 99% and 48% in 2017 and 2018, respectively. The difference in removal efficiencies can be attributed to the much longer residence times and greater organic carbon (OC) availability in the bioreactor in 2017. While the long residence times in 2017 resulted in nearly complete denitrification with reduced concentrations of the greenhouse gas nitrous oxide in the bioreactor outflow, it also led to very strongly reduced conditions with production of methane (another greenhouse gas) and hydrogen sulphide ("rotten egg smell"). The shorter residence times occurring in 2018 following the modification of the bioreactor inlet manifold rectified this strongly reduced condition; however the nitrate removal efficiency concomitantly decreased. Elevated discharges of OC and dissolved reactive phosphorus (DRP) were evident during the first start-up phase of the bioreactor in 2017. In 2018 significant removal (89%) of DRP was measured over the drainage season, with no initial elevated DRP discharge. Ongoing investigations aim to optimise installation costs and treatment efficiency, while minimising any potential side effects. Specifically, options to improve the poor treatment during high flows will be investigated in the 2019 drainage season (e.g. by adding readily available OC source such as methanol).
... Factors such as water temperature, residence time, and the carbon substrate affect the removal rate of nitrate. Hartz (51) showed that denitrification rates can be greatly increased by adding a carbon source such as glycerin and methanol. Various carbon substrates have been evaluated for bioreactors, including sawdust, straw, corn stalks, cardboard fiber, and compost; however, materials that are porous and have a high hydraulic conductivity, such as wood waste, are less likely to impede the flow of water and are easier to maintain. ...
... Water in WC microcosms was brown colored during operation; the highest intensity of brown colored water was observed in O-WC, followed by E-WC and P-WC. This was due to tannins leached from the WC (Hartz et al., 2017). Although colored water is not necessarily a disadvantage for fish performance, clear water could enhance the ability of fish to capture feed and therefore lead to enhanced growth and improved feed conversion ratios; and allows the farmer to observe fish health, behavior, and feeding activity (Davidson et al., 2016). ...
Article
There is a lack of information on denitrification of saline wastewaters, such as those from marine recirculating aquaculture systems (RAS), ion exchange brines and wastewater in areas where sea water is used for toilet flushing. In this study, side-by-side microcosms were used to compare methanol, fish waste (FW), wood chips, elemental sulfur (S0) and a combination of wood chips and sulfur for saline wastewater denitrification. The highest denitrification rate was obtained with methanol (23.4 g N/(m3·d)), followed by FW (4.5 g N/(m3·d)), S0 (3.5 g N/(m3·d)), eucalyptus mulch (2.6 g N/(m3·d)), and eucalyptus mulch with sulfur (2.2 g N/(m3·d)). Significant differences were observed in denitrification rate for different wood species (pine > oak ≫ eucalyptus) due to differences in readily biodegradable organic carbon released. A pine wood-sulfur heterotrophic-autotrophic denitrification (P-WSHAD) process provided a high denitrification rate (7.2-11.9 g N/(m3·d)), with lower alkalinity consumption and sulfate generation than sulfur alone.
... The Submersible Ultraviolet Nitrate Analyzer (SUNA, Sea-Bird Scientific, Bellevue, Washington) is an optical sensor that measures nitrate-N concentrations in-situ , with no purge sampling required. Field investigations using the SUNA have mostly been limited to marine and estuarine environments (e.g., Johnson and Coletti 2002 ;Macintyre et al. 2009 ;O'Boyle et al. 2014 ;Poornima et al. 2016 ) with some applications in surface water (Sackmann 2011 ;Wiebe et al. 2015 ;Duncan et al. 2017 ;Hartz et al. 2017 ) and only one published application to date in groundwater wells (Opsahl et al. 2017 ). The SUNA was used to reveal rapid changes in groundwater nitrate-N concentrations following recharge events in two karst bedrock wells through longterm (>1 year) hourly monitoring. ...
Article
Optical sensors are promising for collecting high resolution in-well groundwater nitrate monitoring data. Traditional well purging methods are labor intensive, can disturb ambient conditions and yield an unknown blend of groundwater in the samples collected, and obtain samples at a limited temporal resolution (i.e., monthly or seasonally). This study evaluated the Submersible Ultraviolet Nitrate Analyzer (SUNA) for in-well nitrate monitoring through new applications in shallow overburden and fractured bedrock environments. Results indicated that SUNA nitrate-N concentration measurements during flow cell testing were strongly correlated (R 2 = 0.99) to purged sample concentrations. Vertical profiling of the water column identified distinct zones having different nitrate-N concentrations in conventional long-screened overburden wells and open bedrock boreholes. Real-time remote monitoring revealed dynamic responses in nitrate-N concentrations following recharge events. The monitoring platform significantly reduced labor requirements for the large amount of data produced. Practitioners should consider using optical sensors for real-time monitoring if nitrate concentrations are expected to change rapidly, or if a site's physical constraints make traditional sampling programs challenging. This study demonstrates the feasibility of applying the SUNA in shallow overburden and fractured bedrock environments to obtain reliable data, identifies operational challenges encountered, and discusses the range of insights available to groundwater professionals so they will seek to gather high resolution in-well monitoring data wherever possible.
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One of the most important problems in drainage systems is the leaching of nitrate and its entry into surface water resources. Increased concentration of nitrate in water resources causes health problems to human and animals. The denitrification process, as one of the suitable solutions for nitrate removal from contaminated water, faces restrictions in agricultural soils due to lack of the carbon materials. Providing carbon in the soil promotes the process and removes more nitrate from the environment. The use of organic materials as cheap and affordable carbon is one of the best options for this purpose. In fact, biofuel reactor are a simple and relatively inexpensive technology in which carbon sources are used to facilitate denitrification. The intensity of denitrification in biological reactors depends on the type of carbon source, temperature, water soluble oxygen, hydraulic residence time and hydraulic parameters. Studies have shown that biological reactors are capable of removing up to 99 percent of nitrates in agricultural drainage. In recent years, numerous studies have been accomplished on the use of biological reactors and their ability and how they are applied to remove nitrates. In this paper, biological bioreactors of denitrification have been investigated as a method for removing nitrate from agricultural drainage.
Article
The negative impact of agriculture on the quality of local water streams is widely recognized. Fertilizer residues not taken up by the crops leach into the drainage water and enter the surface water, resulting in eutrophication. Despite various initiatives to prevent this leaching by optimizing fertilizer schemes, the desired effect was not achieved, and the focus has shifted to denitrifying end-of-pipe techniques. Because the available area for installing such treatment systems is often limited, the development of intensified systems is a trend that has emerged recently. In this scope, the main goal of this study was therefore to investigate the suitability of a denitrifying Moving Bed Bioreactor (MBBR) as a low footprint technology, which can compete with conventional technologies. Two parallel lab-scale pilot MBBRs, one at low temperature and one at ambient temperature, were operated for 850 days to investigate the effectiveness and robustness under changing process parameters (hydraulic retention time (HRT), temperature, shutdown). Eventually, the system was scaled up to a full-scale installation and monitored during a full drainage season in the field. The pilot-scale MBBRs achieved removal efficiencies above 90% under optimal conditions (high C/N ratio and minimal HRT of 8 h), even while operating at low temperatures. The robustness of the system was also demonstrated by the immediate start-up after a shutdown period of 220 days. Overall, the full-scale MBBR treated 2910.1 m³ drainage water and removed approximately 59 kg NO3-N. Unfortunately, the average removal efficiency, i.e., 70%, was lower than the lab-scale system, but by intensifying the mixing in the MBBR, improved results were obtained. Nitrite accumulation was furthermore also prevented.
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Denitrifying “woodchip” bioreactors are engineered systems, consisting of a carbon filled trench (e.g., with woodchips), designed to remediate nitrogen (N)-enriched water through naturally occurring denitrification, a process where microbes reduce nitrate into inert di-nitrogen gas during their respiration processes. Recent studies have demonstrated the feasibility of woodchip bioreactors for treating aquacultural wastewater, specifically the concentrated effluents generated from recirculating aquaculture (RAS), with the caveat that system lifespan can be reduced from clogging associated with high organic solids loading and bacterial overgrowth. Because this technology is relatively new, particularly for aquaculture applications, lifetime cost-efficiency has not been fully assessed. A cost-estimate of N removal over a one- to five-year anticipated lifespan was obtained by estimating initial capital, recurring, and operational expenditures of a full-scale bioreactor system designed for a RAS production facility, using N removal rates from previous pilot-scale aquaculture wastewater bioreactor research. Assumptions included static N removal rates of 6.06 or 11.75 kg of N removal per year for conservative and maximum sensitivities, respectively 49 and 71% N removal efficiency, and at least one woodchip replacement over the system lifetime across a ten-year planning horizon. Initial capital expenditure totaled $47,838 or roughly $139.88 per m³ installed with woodchip replacements each $19,469. Ten-year operational expenditure total present value costs included of $3737 for water quality work and $4666 for lifetime maintenance. Cost per kg of N removed per year ranged from $13.35 to $2.83, dependent on woodchip replacement scenarios of one- to five-years, respectively, which demonstrated denitrification bioreactors might offer a low-cost N treatment option for aquacultural farmers.
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A spectrophotometric procedure for determination of nitrate in water, soil extracts, and a variety of other sample types is described using one reagent solution which is easily prepared and stored. Sample and equipment requirements are minimal. Reduced chemical hazard, simplicity, and versatility represent improvements over existing methods. Limit of detection is 0.01 µg N mL (0.72 μM ) or less, depending on the matrix.
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Nitrate from agricultural activity contributes to nutrient loading in surface water bodies such as the Mississippi River. This study demonstrates a novel in-stream bioreactor that uses carbonaceous solids (woodchips) to promote denitrification of agricultural drainage. The reactor (40 m3) was trenched into the bottom of an existing agricultural drainage ditch in southern Ontario (Avon site), and flow was induced through the reactor by construction of a gravel riffle in the streambed. Over the first 1.5 yr of operation, mean influent NO3-N of 4.8 mg L(-1) was attenuated to 1.04 mg L(-1) at a mean reactor flow rate of 24 L min(-1). A series of flow-step tests, facilitated by an adjustable height outlet pipe, demonstrated that nitrate mass removal generally increased with increasing flow rate. When removal rates were not nitrate-limited, areal mass removal ranged from 11 mg N m(-2) h(-1) at 3 degrees C to 220 mg N m(-2) h(-1) at 14 degrees C (n = 27), exceeding rates reported for some surface-flow constructed wetlands in this climatic region by a factor of about 40. Over the course of the field trial, reactor flow rates decreased as a result of silt accumulation on top of the gravel infiltration gallery. Design modifications are currently being implemented to mitigate the effects of siltation. In-stream reactors have the potential to be scaled larger and could be more manageable than attempting to address nitrate loading from individual tile drains. They could also work well in combination with other nitrate control techniques.
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In coastal California nitrogen (N) in runoff from urban and agricultural land is suspected to impair surface water quality of creeks and rivers that discharge into the Monterey Bay Sanctuary. However, quantitative data on the impacts of land use activities on water quality are largely limited to unpublished reports and do not estimate N loading. We report on spatial and temporal patterns of N concentrations for several coastal creeks and rivers in central California. During the 2001 water year, we estimated that the Pajaro River at Chittenden exported 302.4 Mg of total N. Nitrate-N concentrations were typically <1 mg N l(-1) in grazing lands, oak woodlands, and forests, but increased to a range of 1 to 20 mg N l(-1) as surface waters passed through agricultural lands. Very high concentrations of nitrate (in excess of 80 mg N l(-1)) were found in selected agricultural ditches that received drainage from tiles (buried perforated pipes). Nitrate concentrations in these ditches remained high throughout the winter and spring, indicating nitrate was not being flushed out of the soil profile. We believe unused N fertilizer has accumulated in the shallow groundwater through many cropping cycles. Results are being used to organize landowners, resource managers, and growers to develop voluntary monitoring and water quality protection plans.
Article
Trials were conducted in 15 commercial fields in the central coast region of California in 1999 and 2000 to evaluate the use of presidedress soil nitrate testing (PSNT) to determine sidedress N requirements for production of iceberg and romaine lettuce (Lactuca sativa L.). In each field a large plot (0.2-1.2 ha) was established in which sidedress N application was based on presidedress soil NO3-N concentration. Prior to each sidedress N application scheduled by the cooperating growers, a composite soil sample (top 30 cm) was collected and analyzed for NO3-N. No fertilizer was applied in the PSNT plot at that sidedressing if NO3-N was >20 mg.kg-1; if NO3-N was lower than that threshold, only enough N was applied to increase soil available N to ≈20 mg.kg-1. The productivity and N status of PSNT plots were compared to adjacent plots receiving the growers' standard N fertilization. Cooperating growers applied a seasonal average of 257 kg.ha-1 N, including one to three sidedressings containing 194 kg.ha-1 N. Sidedressing based on PSNT decreased total seasonal and sidedress N application by an average of 43% and 57%, respectively. The majority of the N savings achieved with PSNT occurred at the first sidedressing. There was no significant difference between PSNT and grower N management across fields in lettuce yield or postharvest quality, and only small differences in crop N uptake. At harvest, PSNT plots had on average 8 mg.kg-1 lower residual NO3-N in the top 90 cm of soil than the grower fertilization rate plots, indicating a substantial reduction in subsequent NO3-N leaching hazard. We conclude that PSNT is a reliable management tool that can substantially reduce unnecessary N fertilization in lettuce production.
Article
As concern over NO3-N pollution of ground water increases, California lettuce growers are under pressure to improve nitrogen (N) fertilizer efficiency. Crop growth, N uptake, and the value of soil and plant N diagnostic measures were evaluated in 24 iceberg and romaine lettuce (Lactuca sativa L. var. capitata L., and longifolia Lam., respectively) field trials from 2007 to 2010. The reliability of presidedressing soil nitrate testing (PSNT) to identify fields in which N application could be reduced or eliminated was evaluated in 16 non-replicated strip trials and five replicated trials on commercial farms. All commercial field sites had greater than 20 mg·kg-1 residual soil NO3-N at the time of the first in-season N application. In the strip trials, plots in which the cooperating growers' initial sidedress N application was eliminated or reduced were compared with the growers' standard N fertilization program. In the replicated trials, the growers' N regime was compared with treatments in which one or more N fertigation through drip irrigation was eliminated. Additionally, seasonal N rates from 11 to 336 kg·ha-1 were compared in three replicated drip-irrigated research farm trials. Seasonal N application inthestriptrialswasreducedbyanaverageof77kg·ha-1 (73kg·ha-1 vs. 150kg·ha-1 for the grower N regime) with no reduction in fresh biomass produced and only a slight reduction in crop N uptake (151 kg·ha-1 vs. 156 kg·ha-1 for the grower N regime). Similarly, an average seasonal N rate reduction of 88 kg·ha-1 (96 kg·ha-1vs. 184 kg·ha-1) was achieved in the replicated commercial trials with no biomass reduction. Seasonal N rates between 111 and 192 kg·ha-1maximized fresh biomass in the research farm trials, which were conducted in fields with lower residual soil NO3-N than the commercial trials. Across fields, lettuce N uptake was slow in the first 4 weeks after planting, averaging less than 0. 5 kg·ha-1·d-1. N uptake then increased linearly until harvest (≈ 9 weeks after planting), averaging ≈ 4 kg·ha-1·d-1over that period. Whole plant critical N concentration (Nc, the minimum whole plant N concentration required to maximize growth) was estimated by the equation Nc(g·kg-1) = 42 L 2. 8 dry mass (DM, Mg·ha-1); on that basis, critical N uptake (crop N uptake required to maintain whole plantNaboveNc)inthecommercialfieldsaveraged116kg·ha-1comparedwiththemean uptake of 145 kg·ha-1with the grower N regime. Soil NO3-N greater than 20 mg·kg-1 was a reliable indicator that N application could be reduced or delayed. Neither leaf N nor midrib NO3-N was correlated with concurrently measured soil NO3-N and therefore of limited value in directing in-season N fertilization.
Article
Trials in nine commercial celery (Apium graveolens L.) fields were conducted between 1997-99 to evaluate grower drip irrigation management practices and their effects on yield and quality. Surface drip irrigation tapes with flow rates higher and lower than the grower-installed tapes were spliced into the field system; as the cooperating growers irrigated and applied N fertigation according to their routine practices these drip tapes delivered either more or less water and N than the field drip system. Total grower water application during the drip-irrigated portion of the season ranged from 85% to 414% of seasonal reference evapotranspiration (ETo). Water volume per irrigation varied among fields from 1.8 to 3.8 cm, with irrigation frequency varying from an average of every other day to once a week. Grower management of drip irrigation was not consistently successful in maintaining soil water tension (SWT) in a desirable range. SWT was often below -30 kPa, and in some cases below -70 kPa. These transient stresses were more often a result of inappropriate irrigation frequency than applied water volume. In four of the fields plots receiving less water than that delivered by the field system produced equivalent marketable yield and quality, indicating a significant potential for water savings. An economically important incidence of petiole pithiness (collapse of parenchyma tissue) was observed in four fields. Infrequent irrigation under high ETo summer conditions, rather than irrigation volume applied, appeared to be the major factor in pith development. N fertigation amount and crop N status appeared to be unrelated to pithiness severity. We conclude that celery drip irrigation management could be substantially improved by maintaining a closer proportionality between irrigation and crop evapotranspiration (ETc), increasing irrigation frequency, and reducing volume per irrigation.
Article
Loss of nitrate in subsurface drainage water from agricultural fields is an important problem in the Midwestern United States and elsewhere. One possible strategy for reducing nitrate export is the use of denitrification bioreactors. A variety of experimental bioreactor designs have been shown to reduce nitrate losses in drainage water for periods up to several years. This research reports on the denitrification activity of a wood chip-based bioreactor operating in the field for over 9 years. Potential denitrification activity was sustained over the 9-year period, which was consistent with nitrate removal from drainage water in the field. Denitrification potentials ranged from 8.2 to 34 mg N kg−1 wood during the last 5 years of bioreactor operation. Populations of denitrifying bacteria were greater in the wood chips than in adjacent subsoil. Loss of wood through decomposition reached 75% at the 90–100 cm depth with a wood half-life of 4.6 years. However, wood loss was less than 20% at 155–170 cm depth and the half-life of this wood was 36.6 years. The differential wood loss at these two depths appears to result from sustained anaerobic conditions below the tile drainage line at 120 cm depth. Pore space concentrations of oxygen and methane support this conjecture. Nitrous oxide exported in tile water from the wood chip bioreactor plots was not significantly higher than N2O exports in tile water from the untreated control plots, and loss of N2O from tile water exiting the bioreactor accounted for 0.0062 kg N2O-N kg−1 NO3-N.
Article
A 5-year-old wood particle reactor treating agricultural tile drainage in southern Ontario was monitored for its ongoing ability to treat both nitrate (NO3–) and perchlorate (ClO4–). Prior to sampling undertaken in the fifth year of operation, a highway safety flare containing ClO4– was immersed in the inlet pipe elevating influent ClO4– concentrations to up to 33.7 μg/L. ClO4– removal rates were inhibited in the presence of more than 1 to 2 mg/L NO3–-N, but increased rapidly to about 60 μg/L/d upon NO3– depletion. Nitrate removal rates, measured subsequently in the sixth and seventh years of operation, varied with temperature in the range of 2 to 16 mg N/L/d, but remained similar to rates measured in the second year. Additionally, no deterioration in the hydraulic conductivity (K) of the coarse core layer (0.5 <K < 5 cm/s) was detected over the monitoring period. These results demonstrate that coarse wood particle media can deliver stable NO3– removal rates and can remain highly permeable over a number of years. The media can also provide high removal rates for other redox sensitive contaminants such as ClO4–. The ability to directly measure the reactor flow rate, in this case via an outlet pipe, greatly simplified the task of estimating hydraulic properties and reaction rates.
Article
Subsurface horizontal flow constructed wetlands are being evaluated for nitrogen (N) and phosphorus (P) removal from wastewater in this study through different gravel sizes, plant densities (Iris pseudacorus), effects of retention times (1 to 10 days) on N and P removal in continuously fed gravel wetland. The inlet and outlet samples were analyzed for TKN, NH4-N, and NO3-N, as standard methods. The planted wetland reactor with fine (SG) and coarse (BG) gravels removed 49.4% and 31.4% TKN, respectively, while unplanted reactors removed 43.4% and 26.8% TKN. Also, the efficiencies for NH4-N were 36.7–43% and 21.6–25.4% for SG and BG planted reactors, respectively. The efficiencies for NO3-N were 53.5–62.5% and 21.6–25.4% for SG and BG planted reactors, respectively. Roles of plants in SG reactors for O-PO4 were 5–12% and 3–8% in BG. Also, the roles of plants in the reactors for TP were 9% and 7.4%. The minimum effective detention time for the removal of NO3-N was 4–5 days. The subsurface constructed wetlands planted with I. pseudacorus can be an appropriate alternative in wastewater treatment natural system in small communities.
Article
Two 200-L fixed-bed bioreactors, containing porous-medium material of coarse sand and organic carbon (tree bark, wood chips and leaf compost), were used to treat NO3 contamination from agricultural runoff. Flow from a farm-field drainage tile containing NO3-N concentrations of 3–6 mg L−1 was successfully treated in the reactors (NO3-N < 0.02 mg L−1) at a rate of 10–60 L day−1 over a 1-yr period. Treatment occurs by anaerobic denitrification promoted by the added solid-phase organic carbon. Because the reactor design is simple, economical to construct and maintenance free, it may provide a practical solution to the problem of treating redox-sensitive contaminants, such as NO3, in agricultural runoff.
Article
The design for an in situ ultraviolet spectrophotometer (ISUS) that can operate while submerged to depths of at least 2000 m is reported. We show that the ISUS can be used to make high resolution (∼1/s and 0.5 cm) and long-term (>3 months) measurements of the concentration of nitrate, bisulfide and bromide in seawater using the distinctive, ultraviolet absorption spectra of these chemical species. The precision, accuracy and stability of the chemical concentrations derived with the ISUS are sufficient for many biogeochemical studies. One standard deviation of the nitrate concentration in seawater is ∼0.5 μM and the limit of detection (3 SD) for one observation would be ∼1.5 μM. However, the noise is nearly random and significant reductions in the detection limit are possible by averaging multiple observations. The 95% confidence interval for a 30 s scan is 0.2 μM. Low temperatures appear to produce a bias (∼10% at 400 m depth in the ocean) in the nitrate concentration and in the salinity estimated from the bromide concentration. If an independent estimate of salinity is available, then the bias in nitrate can be eliminated by correcting nitrate concentrations by the same amount that the optical estimate of salinity is in error. The instrument has been deployed on a mooring in the equatorial Pacific for a 6-month period with no apparent degradation in performance during the first 3 months. Measurements of UV spectra at a height of 1 cm over the bottom in a cold seep at 960 m depth demonstrate the capability to detect bisulfide ion within the benthic boundary layer.
Article
Simple technologies that remove nitrate from effluents and other point discharges need to be developed to reduce pollution of receiving waters. Denitrification beds are lined containers filled with organic carbon (typically wood chip or coarse sawdust) and are a technology that is proving promising. Water containing NO3− (treated effluent or agricultural drainage) is passed through the bed and the wood chips act as an energy source for denitrifying bacteria that convert NO3− to N gases. There are few data on the efficiency of NO3 removal in large-scale beds. We report here NO3− removal results from three large denitrification beds with volumes of 83, 294, and 1320 m3 treating dairy shed effluent, treated domestic effluent and glasshouse effluent, respectively. Nitrate was nearly completely removed from the dairy shed effluent (annual load of 31 kg N) and domestic effluent (annual load 365 kg N). In these beds, NO3− removal, presumably by denitrification, was limited by NO3− concentration. However, the bed treating glasshouse effluent was overwhelmed by very high NO3− concentration (about 250 g N m−3) and high flow rates (about 150 m3 d−1) but still reduced NO3− concentration to about 150 g N m−3. For this bed, long-term NO3− removal was between 5 and 10 g N m−3 of bed material when NO3− was non-limiting and was similar to rates reported for other smaller denitrification beds. As expected, organic N, ammonium and phosphorus were not removed from any of the effluents following passage through the beds. Our results suggest that denitrification beds are a relatively inexpensive system to construct and operate, and are suitable for final treatment of a range of NO3−-laden effluents.
Article
Low-cost and simple technologies are needed to reduce watershed export of excess nitrogen to sensitive aquatic ecosystems. Denitrifying bioreactors are an approach where solid carbon substrates are added into the flow path of contaminated water. These carbon (C) substrates (often fragmented wood-products) act as a C and energy source to support denitrification; the conversion of nitrate (NO3−) to nitrogen gases. Here, we summarize the different designs of denitrifying bioreactors that use a solid C substrate, their hydrological connections, effectiveness, and factors that limit their performance. The main denitrifying bioreactors are: denitrification walls (intercepting shallow groundwater), denitrifying beds (intercepting concentrated discharges) and denitrifying layers (intercepting soil leachate). Both denitrifcation walls and beds have proven successful in appropriate field settings with NO3− removal rates generally ranging from 0.01 to 3.6 g N m−3 day−1 for walls and 2–22 g N m−3 day−1 for beds, with the lower rates often associated with nitrate-limitations. Nitrate removal is also limited by the rate of C supply from degrading substrate and removal is operationally zero-order with respect to NO3− concentration primarily because the inputs of NO3− into studied bioreactors have been generally high. In bioreactors where NO3− is not fully depleted, removal rates generally increase with increasing temperature. Nitrate removal has been supported for up to 15 years without further maintenance or C supplementation because wood chips degrade sufficiently slowly under anoxic conditions. There have been few field-based comparisons of alternative C substrates to increase NO3− removal rates but laboratory trials suggest that some alternatives could support greater rates of NO3− removal (e.g., corn cobs and wheat straw). Denitrifying bioreactors may have a number of adverse effects, such as production of nitrous oxide and leaching of dissolved organic matter (usually only for the first few months after construction and start-up). The relatively small amount of field data suggests that these problems can be adequately managed or minimized. An initial cost/benefit analysis demonstrates that denitrifying bioreactors are cost effective and complementary to other agricultural management practices aimed at decreasing nitrogen loads to surface waters. We conclude with recommendations for further research to enhance performance of denitrifying bioreactors.
Article
Denitrification beds are containers filled with wood by-products that serve as a carbon and energy source to denitrifiers, which reduce nitrate (NO(3)(-)) from point source discharges into non-reactive dinitrogen (N(2)) gas. This study investigates a range of alternative carbon sources and determines rates, mechanisms and factors controlling NO(3)(-) removal, denitrifying bacterial community, and the adverse effects of these substrates. Experimental barrels (0.2 m(3)) filled with either maize cobs, wheat straw, green waste, sawdust, pine woodchips or eucalyptus woodchips were incubated at 16.8 °C or 27.1 °C (outlet temperature), and received NO(3)(-) enriched water (14.38 mg N L(-1) and 17.15 mg N L(-1)). After 2.5 years of incubation measurements were made of NO(3)(-)-N removal rates, in vitro denitrification rates (DR), factors limiting denitrification (carbon and nitrate availability, dissolved oxygen, temperature, pH, and concentrations of NO(3)(-), nitrite and ammonia), copy number of nitrite reductase (nirS and nirK) and nitrous oxide reductase (nosZ) genes, and greenhouse gas production (dissolved nitrous oxide (N(2)O) and methane), and carbon (TOC) loss. Microbial denitrification was the main mechanism for NO(3)(-)-N removal. Nitrate-N removal rates ranged from 1.3 (pine woodchips) to 6.2 g N m(-3) d(-1) (maize cobs), and were predominantly limited by C availability and temperature (Q(10) = 1.2) when NO(3)(-)-N outlet concentrations remained above 1 mg L(-1). The NO(3)(-)-N removal rate did not depend directly on substrate type, but on the quantity of microbially available carbon, which differed between carbon sources. The abundance of denitrifying genes (nirS, nirK and nosZ) was similar in replicate barrels under cold incubation, but varied substantially under warm incubation, and between substrates. Warm incubation enhanced growth of nirS containing bacteria and bacteria that lacked the nosZ gene, potentially explaining the greater N(2)O emission in warmer environments. Maize cob substrate had the highest NO(3)(-)-N removal rate, but adverse effects include TOC release, dissolved N(2)O release and substantial carbon consumption by non-denitrifiers. Woodchips removed less than half of NO(3)(-) removed by maize cobs, but provided ideal conditions for denitrifying bacteria, and adverse effects were not observed. Therefore we recommend the combination of maize cobs and woodchips to enhance NO(3)(-) removal while minimizing adverse effects in denitrification beds.
Article
Denitrification beds are a cost-effective technology for removing nitrate from point source discharge. To date, field trials and operational beds have primarily used wood media as the carbon source; however, the use of alternative more labile carbon media could provide for increased removal rate, lower installation costs and reduced bed size. While previous laboratory experiments have investigated the potential of alternative carbon sources, these studies were typically of short duration and small scale and did not necessarily provide reliable information for denitrification bed design purposes. To address this issue, we compared nitrate removal, hydraulic and nutrient leaching characteristics of nine different carbon substrates in 0.2 m³ barrels, at 14 and 23.5 °C over a 23-month period. Mean nitrate removal rates for the period 10–23 months were 19.8 and 15 g N m⁻³ d⁻¹ (maize cobs), 7.8 and 10.5 g N m⁻³ d⁻¹ (green waste), 5.8 and 7.8 g N m−³ d⁻¹ (wheat straw), 3.0 and 4.9 g N m−3 d−1 (softwood), and 3.3 and 4.4 g N m−³ d⁻¹ (hardwood) for the 14 and 23.5 °C treatments, respectively. Maize cobs provided a 3–6.5-fold increase in nitrate removal over wood media, without prohibitive decrease in hydraulic conductivity, but had higher rates of nutrient leaching at start-up. Significant difference in removal rate occurred between the 14 and 23.5 °C treatments, with the mean Q₁₀ temperature coefficient = 1.6 for all media types in the period 10–23 months.
Biological denitrification Nitrogen in Agricultural Systems
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Coyne MS. 2008. Biological denitrification. In: Schepers JS, Raun W (eds.). Nitrogen in Agricultural Systems. Monograph 49, American Society of Agronomy, Madison, WI. p 197–249.
Remediation of Tile Drain Water Using Denitrification Bioreactors. CDFA-FREP Final Report
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Optical Techniques for the Determination of Nitrate in Environmental Waters: Guidelines for Instrument Selection, Operation, Deployment, Maintenance, Quality Assurance, and Data Reporting
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Deschutes River Continuous Nitrate Monitoring. Washington State Department of Ecology Publication
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Sackmann BS. 2011. Deschutes River Continuous Nitrate Monitoring. Washington State Department of Ecology Publication 11-03-030. https://fortress.wa.gov/ecy/ publications/documents/1103030.pdf (accessed May 16, 2016).